A small two-cycle internal combustion engine used as a driving source for portable equipment such as a chain saw, a brush cutter and the like is equipped with a diaphragm type carburetor so that excellent operation of the internal combustion engine may be controlled in any attitude.
As disclosed in Japanese Patent Application Laid-Open Publication No. 35047/1987, there is proposed an arrangement wherein when the engine is started, fuel is supplied from a fuel tank to a metering chamber by a manual primer pump, the fuel being also directed to fill an accumulator chamber. A button of an accumulator is operated simultaneously with the pull start operation of the engine to move the fuel in the accumulator through a fuel nozzle to an air intake passage of a carburetor. However, recently, internal combustion engines have been equipped with a battery driven starter motor mounted on the aforementioned portable equipment. It has become desirable that a power supply for driving the starter motor is also utilized to automatically perform a series of operations.
In view of the foregoing, reference is again made to pending U.S. application Ser. No. 237,964 in which there is disclosed an arrangement wherein a fuel reservoir formed from a resilient container is provided between a volume type primer pump and a fuel tank, whereby during the normal rotation of the primer pump, fuel in the metering chamber is replenished to the fuel reservoir by the primer pump and extra fuel is returned to the fuel tank, while, during the reverse rotation of the primer pump, the fuel in the fuel reservoir is injected as a start-fuel through a resiliently deformed portion of the fuel reservoir to an intake passage of a carburetor.
However, in this start-fuel supply device, the start fuel is metered by the resilient deformation of the fuel reservoir, and, therefore, the resilient deformation gives rise to unevenness due to the difference of the strength of resiliency, size and shape of the fuel reservoir, and the suction force of the primer pump, and the like. It has been found from the above-described fact to be difficult to accurately meter the start fuel as required. Furthermore, when a switch of the battery operated starter motor is turned off after the engine has been started, the primer pump operatively associated therewith also stops but the check valve remains closed, and therefore, fuel in the primer pump is returned through the expansion of the fuel reservoir and a small amount of fuel flows into the fuel reservoir.
At the time of restarting the engine immediately after the operation of the engine has been terminated, no start fuel is required. However, the temperature of the engine sometimes is not so high that the temperature switch is actuated, in which case, when the starter motor is driven, the primer pump is reversely rotated with the result that a small amount of start fuel remaining in the fuel reservoir is injected out of the fuel nozzle, which sometimes deteriorates the startability. If the engine is well heated, the temperature switch is opened so that the primer pump is not reversely rotated, and the start fuel is not supplied. That is, in the aforementioned device, a reaction in a temperature region where the temperature switch is closed cannot be made immediately after the operation of the engine has been terminated, and, therefore, the small amount of the start fuel remaining in the fuel reservoir is injected out of the fuel nozzle every time the starter cell motor is driven.